


UnderKnight / FairyTale

by LovelyKouga



Category: Undertale (Video Game)
Genre: Ecto-Penis, Ecto-Tongue, Fontcest, Fucking on the throne, Incest, Initiation, M/M, Undertail, Undertale AU, desecration, fairytale, the thrill of almost getting caught, underknight, voyeristic undertones
Language: English
Status: Completed
Published: 2016-04-13
Updated: 2016-04-13
Packaged: 2018-06-02 01:19:09
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,796
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6544591
Author URL: https://archiveofourown.org/users/LovelyKouga/pseuds/LovelyKouga
Summary: <blockquote class="userstuff">
              <p>My own Medieval AU where Sans is a Knight (abeit a lazy one), and Papyrus finally achieves his dream of becoming a Royal Guard.</p>
<p>Papyrus is strutting his stuff in his new uniform, but he's about to find out that there's more to being accepted as a fully-fledged member than just donning the uniform. In order to gain rapport with his new peers (and popularity!), he must complete the 'traditional' initiation. Sans is just the one to walk him though it, after all, he has been a Knight for many years now.</p>
            </blockquote>





	UnderKnight / FairyTale

**Author's Note:**

> My thoughts about my AU:  
> \- The Underground is actually flourishing! Mostly thanks to Queen Toriel blasting a hole in the ceiling and letting light through.  
> \- Asgore is a disgraced King, and has been banished.  
> \- Sans used to be the Royal Fool, but after protecting The Queen and her adopted child (Frisk) from an assassination attempt by the Malevolent Flowey, she grants him a Knighthood. He's fine with this, as it usually involves sitting at the Queen's side all day...  
> \- Frisk refuses to adhere to gender roles, and will be neither a pretty Princess nor a battling Prince. But at the same time, they're both?  
> \- Alphys is a witch, but keeps white dogs instead of black cats and is pretty proficient at potions. Bit of a Fairytale buff.  
> \- Undyne is the Captain of the Royal Guard, and now, papyrus finally joins the ranks! He is a rookie greenhorn, and his new mission is to learn how to be an effective and beloved member of the Royal Guard.  
> \- Grillby owns a pub / brothel. 'Nuff said.  
> \- Muffit 'works' at said brothel, but is more of a swindler/spymaster and has an army of spies. Sex just happens to be a good way to get information - and money, out of people.  
> \- Mettaton is a wizard of sorts, although it's mostly just for show and his 'magic' used to bedazzle and amaze during his shows is actually just concoctions Alphys made for him. Smoke and mirrors type stuff.

“It looks like it was made for me!” He stated, proudly doing a twirl on the spot. He couldn’t seem to tear his eyes away from his Guardly visage, so much so that his head stayed facing the mirror as his neck vertebra dislocated, enabling his body to do a full spin while allowing a full view of his entire body from every angle. It was very much akin to ‘The Exorcist’, or perhaps an owl. An adorable, skeletal owl.

Sans had to chuckle at that imagery. “it does look like it was made for you, bro…probably because it was.”

“Thank you, brother!” Papyrus beamed at him, hearing only the compliment. His selective hearing knew no bounds.

“no you don’t understand it was literally made for you-“

“An outfit this strapping, it is befitting that a monster just as strapping is to wear it!”

“they took your measurements and everything-“

“Greatness cannot be measured with mere metric fancies!”

“HOW do you not remember that-?”

Papyrus excitedly grabbed at the bottom of the long, red cape, and drew it fully around himself before throwing it behind him dramatically. Amazingly, it billowed and almost seemed to blow in the wind…which was a feat in itself, considering that the Underground was kinda…under the ground. He struck his very best superhero pose, the kind that Alphys’ Fairytale heroes tended to favor, puffing his chest out and grinning at his reflection. The older brother didn’t fail to notice the way that his eye sockets welled up with pride. Sans’ own grin became wider and more genuine than usual as he stood behind Papyrus, admiring him too. He couldn’t help thinking that yes, maybe his babybones bro did look a _little_ bit cool.

Sans often wished he looked like his brother, especially now. With his towering height, defined cheekbones, pure white bones and kind eyesockets, he really did look quite handsome. The pristine Royal Guardsman uniform accentuated his barrel chest, tiny spinal column and jutting hipbones almost obscenely, and for some reason, whoever had designed the skeleton version of this uniform seemed to think that leaving those parts so…bare, was acceptable. Skeleton monsters were rare in the Underground but even so, anyone could tell just by looking at the way the pants hugged around only the bottom half of the pelvis that it was a tad skimpy. Papyrus, bless his innocent soul, almost resembled a ‘strong female character’ in that get-up.

As his own, more tired-looking eyes swept over his brother’s body, Sans felt a strange sensation well up inside of him. He frowned inwardly, attempting to stamp the thoughts that were coming into his skull out before the embers roared into a flame. But his bro wasn’t helping this new situation – he was now slowly pulling off his gloves with his teeth. He discarded one, and used the other to lovingly polish the Royal Crest that gleamed proudly on the front of his chestplate.

“Sans? When do I receive my sword?”

Sans jumped a little, averting his eyes in shame. The faintest of blue blush was forming over his cheeks, and he knew if he talked now, his voice would rasp and croak. Papyrus continued, unperturbed.

“To reach optimal levels of coolness, I shall need to unsheathe my weapon and practise posing with it too!”

Sans collected himself, and focused all of his energy into staying as deadpan as possible. “huh? oh…you get one after you pass your initiation.”

The taller skeleton perked up at that. “Initiation? Oh, that sounds wondrous!” He clasped his hands together animatedly, shifting from left to right foot in a little excited dance. He was even shaking a little, eager for what was to come. “What must I do?”

_Adorable_.

“wellll…” Began Sans, the gears beginning to turn in his skull.  
“first you have to sneak into the throne room, and sit on Queen Toriel’s throne.”

Papyrus’ face snapped into a serious expression instantly. To do such a thing was a beheading offence.  
“But…what if I get caught?”

Sans shrugged. “i wouldn’t worry, bro. everyone had to do it, even me. as long as you time it around the other guards’ rounds, there’s no chance of being caught.”

Papyrus looked unconvinced, but the onset of peer pressure was beginning to cave his resolve.  
“… _Everyone_ has done it?” Papyrus enquired, his voice small and his posture uncertain. He was pressing the tips of his fingers together in a self-concious gesture, and Sans decided that while it was cute, it didn’t suit him.

Sans nodded, the corner of his grin quirking up a little. “it feels really good.”

“Good? How?” Papyrus inquired, tentatively interested.

“well for one, it helps you gain respect with your fellow Guards. and for two?”

Papyrus unconsciously shuffled a little closer. Sans’ expression was…interesting.

But Sans inhaled, holding for dramatic effect, but only replied with a cheeky wink before turning on his heel and padding down the hallway in the direction of the Throne Room. Papyrus didn’t even hesitate; following his brother was just natural for him.

 

***

 

“I will do anything in the name of tradition! If this is what I need to do to become a fully-fledged and accepted member of the Royal Guard, then the Great Papyrus shall follow through!”  
He was saying it more to himself than to anyone else. Papyrus shuffled uncomfortably in place, staring down at the lush purple velvet of the seat of the Royal Throne. He glanced back only once at his brother for moral support, and was rewarded with a thumbs up and reassurance that they had at least half an hour before the next round of guards showed up. The taller skeleton turned around and squeezed his eyesockets shut, hovering for a second over the seat before taking the plunge and finally sitting down. It was very anti-climatic. He had honestly half-expected Captain Undyne to rush in in a blind rage, spears tearing through the air and spearing him straight through the soul for daring to even look at the throne, let alone sit in it. But everything was deathly quiet. He opened one of his sockets a crack, and noticed everything was a tad darker than it was before. The various candles that lined the walls of the great hall had all been extinguished, and Papyrus shivered a little when all he could see of Sans was the glowing pupils as he stepped into view from the darkness. His small form bent at the waist in a solemn bow before the now-quizzical Papyrus.

“my King.” Sans said, tilting his chin up to look his befuddled brother in the eyesockets. “how may i, a lowly Knight, serve you this evening?”

Papyrus spluttered for a minute, before his grin betrayed him. Aha, it must be a roleplay! All a part of the initiation! And he had to admit, he did rather like the sound of ‘King Papyrus’. He sat up a little straighter in his seat, his expression turning haughty and aloof as he stroked an impressive imaginary beard.

“Nyees, my loyal Knight! Tonight, I intend to repay you for your devoted service to protecting my Royal Hiney!”

Sans only just managed to stifle the laughter that bubbled in his throat, dropping character for only a second.

“Your Hiney is too magnificent. i would do anything to your Hiney- i mean, for.”

“Insolence!” Papyrus roared, crossing his arms authoritatively and spreading his knees apart.

Sans shivered.

“For that jape, you shall crawl over here post-haste and lick the Royal Boot!” He was really getting into this, thought Sans as his breathing picked up the pace. The tone Papyrus was using was fucking doing things to his heads. _Yes, both of them_. Obediently, he dropped down onto his knees as instructed, but instead of grovelling pathetically, he crawled forwards slowly and purposefully on hands and knees. His movements were almost catlike, and his hips undulated side-to-side with each agonisingly deliberate stride. Papyrus studied his face with obvious surprise as the smaller skeleton drew nearer, kneeling down in front of his ‘King’. He stared unblinkingly up at Papyrus as he formed his glowing blue tongue between his jaws, before leaning down and languidly painting a thick, blue stripe all the way up the front of Papyrus’ boot. The two locked eyes as Sans’ tongue didn’t stop there – it skated past his knee, thoughtfully pausing over the kneecap before travelling up, up, up…

‘King’ Papyrus could only watch as Sans rose up into a crouching position, allowing him to continue his journey halfway up Papyrus’ bare femur. He left open-jawed, breathy kisses, licks and bites in his wake, and the glowing white pupils never left Papyrus’ face. They would dilate every time he elicted any kind of sound from his brother, and Papyrus looked down at him unsteadily, his face aflame with an orange blush and his knuckles creaking on the armrests with how hard he was digging into them. As Sans neared the junction between the femur and pelvis, he dragged his hands into the inside of Papyrus’ knees, forcing them further apart. He noted with satisfaction that the other skeleton was trembling, and he stroked comforting circles against the inside of his thighs in apology. They were splayed lasciviously, and his breath came out in a loud pant when he bit into Papyrus’ shorts, pulling them down a little with his teeth to expose more bone.

“my King.” Panted Sans, palming at either side of Papyrus’ pelvis. “please tell me, your lowly Knight, what he can do to please you.”

Papyrus shakily opened his jaw to speak, but quickly smothered it with the back of his hand as a series of high moans tumbled forth. Sans froze for a moment before he growled desperately in response, his fangs becoming more prominent. Papyrus felt an odd pressure against the front of his boot, and he glanced down in investigate. Oh god oh god…Sans was…

“M-my Knight-!” He whined, clutching at the front of his cape.

Sans could only huff out a response, as he was currently busy pressing his very large erection against Papyrus’ boot. His brow furrowed as he wrapped one arm around it to keep it in place, before starting up a grinding rhythm with his hips. The faint blue glow throbbed forth from his cock and lit his skull up from underneath, and Papyrus could see every subtle expression on his face as he grinded himself into a stupor. The sight was too much – it wasn’t often that his brother was this open and…vulnerable…

Papyrus leaned back slightly, making room for his hand to plunge into the front of his own shorts. He began to rub in quick little circles as the other hand came to rest on the top of his brother’s skull, petting him fondly. Sans moaned out loud, resting his chin on Papyrus’ knee as he completely came undone. Papyrus’ entire leg began to bounce up and down with the force of his rocking, and his tongue hung sideways out of his fanged jaws in ecstacy. It was so raw, so open. Papyrus fished his own cock out of his shorts – it had now fully formed and jutted out from his pelvis proudly, glowing orange and dripping liberally. The glow seemed to catch Sans’ attention, and his hips stuttered in their rhythm as almost his entire field of vision was taken up by his brother’s dick. His eyes flew open almost comically wide.

“my King…s-sure has some impressive ‘family jewels’.” He managed to pant out.

Papyrus peered disapprovingly down his nosehole at him, trying to keep his expression and voice level.  
“You know puns and jokes were forbidden by me, Knight. Perhaps you need to be…’pun-ished’ for your crimes?” His voice was mock-stern, but his dick twitched at Sans’ obvious turned-on reaction to it. He’d never known Sans had a thing for authority types, but then again…he had never thought about his brother in this way before.

But now, he was just _full_ of ideas.

Sans shakily inclined his head, and Papyrus loved how easy it was to shut him up in this situation. Usually his puns would progressively get worse and worse as Papyrus chased him in a rage around the house, dropping pun after pun as he teleported away just as Papyrus was about to catch him.

Well now who was cat, and who was mouse, nyeh?

Sans shifted position so that he was now knelt between his King’s knees, spreading his fingers across Papyrus’ lower thighs. Papyrus hummed at the attention.  
“Do not move, Knight. Your King, The Great and Powerful Papyrus, must now decide what to do with you.” He instructed, and Sans blushingly nodded, freezing in place as Papyrus made a pleased noise in the back of his throat, and he grasped his dick with one hand, pumping it lazily in front of Sans’ face as he put on a thoughtful expression.

Sans eyed it almost hungrily, his mouth unconsciously opening and his tongue hanging out slightly as Papyrus took his time, playing with himself while Sans watched him with desperate, begging eyes. A single drop of pre-cum fell onto the tip of Sans’ tongue and his pupils practically rolled up into his skull in pleasure. His whole small fame shook like a leaf in the wind as Papyrus teased the head of his cock against his brother’s mouth, and it took all the determination he had in him to resist flicking his tongue against the underside. It was so close, he wanted to taste it so fucking badly, to feel the weight of it on his tongue, feel it slam into the back of his throat, to watch Papyrus come undone.

“Nyeh-heh-heeeh.” Papyrus chuckled darkly, so different from his usual tone. Sans closed his eyes and moaned around his panting, and Papyrus let out a smaller, more reserved sound when he felt Sans’ breath float across the wet tip of his dick. A shudder crawled up the back of his spine as Sans continued to moan, accidentally stimulating him with the hot air huffing against the sensitive glands.

“Knight.” Papyrus heaved, his hips giving an involuntary and very un-king-like jerk.

Sans took that as an order, and whether Papyrus meant it as such or not soon became irrelevant as he felt a hot, impossibly long tongue snake around his member. It appeared to be a prehensile tentacle, because it wrapped itself several times around and drew it into Sans eagerly awaiting mouth. It felt almost…alive. It began to pump the large shaft as Sans took it in as deep as he could, and he looked up adoringly at Papyrus as he moaned around it. The vibrations and the look on the skeleton’s face made Papyrus squirm like a bitch in heat on the throne, and his Kingly façade was stripped away completely when Sans’ wandering fingers found his hole. Two digits entered eagerly, and Papyrus concentrated his magic in that area to accommodate the intruders.

“Haaaa-“ Sans gasped, letting go of Papyrus’ dick with a wet-sounding pant. “my King…you sure are wet down here.” He teased.

Papyrus looked scandalised at the insinuation, but his voice turned into a sharp, clear keen as Sans wiggled his fingers inside him for emphasis.

“i knew you thought i was a royal pain in the ass, bro. A-ahh…hhh…b-but this is gettin’ too literal.”

And with a smirk, his left eye ignited in a burst of blue magic, and Papyrus felt his wrists being restrained on the armrests of the throne by what felt like leather. They slipped and rubbed against his bones, and he moaned over and over as he tugged at them and felt he was unable to move at all. His feet felt heavy, and they shook with pleasure as Sans leaned down, lifting them up over his shoulders. Without any warning, he hungrily plunged his tentacle-tongue into his brother, elicting a breathless, delicious sound that made him physically reel.

“Fffuuuck, bro…” He moaned, his face smushed into the pelvis. His tongue was thrusting shallowly inside, not enough to breach him fully, but enough to make him squirm.  
“Can...ahh, s-shit…can i fuck you?” His voice cracked.

Papyrus’ jaw was hanging wide open. Somewhere amongst it all, he had also materialised a tongue. It was closer to a human’s in size and shape, and he was doing his best to keep it from lolling out of his mouth. He clearly wasn’t used to it, and in the back of his mind, Sans wondered if he had ever conjured one before.

“ _Saaaans_!~” He whined, as his brother’s tongue left his bones. He felt…empty. He wanted to feel full, like before.

“it’s tradition.” Sans drawled, his eyesockets lidding seductively.  
“you…ngh…you wouldn’t want to disappoint your new f-friends, would you?” He finally began fisting at his own cock, and it practically weeped at the attention.

“N-nyeh…Sans, please!” Papyrus tugged at his restraints, moaning again at the sensation of being the one so helpless now.  
“If you promise not to…not to dirty my new outfit…or tell the others that I-I broke character…” He ended, blushing like mad and dropping his gaze to the side as he shyly lifted his hips up off the seat to be at eye-level with Sans.

_“…F-fill me up.”_

Sans stood, his aching knees forgotten as he looked down upon his trembling brother presenting himself.

 

***

“what would Undyne think if she saw the newest member of the Royal Guard-” His hips slammed roughly against Papyrus. “-AHH…Nnh…g-getting FUCKED on the Queen’s throne?”

“S-ANS! AHHNN~ YES!!” Came his unexpected reaction.  
Unexpected for him, anyway. Sans seemed to know just what to say to rile him up.

Papyrus felt… _naughty_. Dirty. Always being the goody-two-shoes in life made even the contemplation of being bad ridiculously exciting. He entertained the thought of Undyne watching him getting ‘speared’ by his own brother, being impaled over and over as, unable to stop as her red eyes scanned their bodies as they actively desecrated the Royal Throne. Papyrus had worked his entire life to be in the Royal Guard, and the combination of risking it all as well as engaging in such lewd acts with his own brother positively thrilled him.

His hips began to move too, meeting Sans’ thrusts halfway as he strained against his bonds, attempting to touch himself. A series of erotic-sounding ‘nyehs’ bubbled forth when Sans leaned over him, still holding onto Papyrus’ bottom half but bracing himself with his other hand on the back of the throne. His tongue licked a tantalising trail up the side of Papyrus’ neck, and he thought he might literally explode into dust from the pleasure. Sans’ voice dropped a few octaves as he practically growled against his ear, the frequency of his profanities speeding up. The rumbling sound of his voice cut through the taller skeleton’s very core, and he slung a leg over Sans’ shoulder, pulling him even closer and even fucking deeper into himself.

“Sans…SsaAAAHns-! A-are you SURE that all new members of the Royal Guard have to do this?” He wasn’t complaining, but in the throes of ecstasy, he was beginning to babble.

“b-bro…i was…’initiated’ for the first time…r-right here. right fucking here b-by the entire Knighthood…” He gasped raggedly at the memory with mixed emotions.  
“i wouldn’t tell ya a…’fibula’, i’m trying tibea honest.”

Papyrus didn’t even react to the pun part, but seemed to slow his hips a little at the confession, opening his eye sockets to look into Sans’ face.

“i-if I didn’t do this first, c-claim you, heh…one of them would eventually get to ya…” He was suddenly very serious.  
“Th’ Royal Guard is not as rosy as you’ve been led to believe. but…I’ll protect ya, Paps. Undyne will too.”

 

_“Sans…no matter what, I love you.”_  
_“Paps, I love you so fucking much.”_

 

They spoke at the same time and looked at each other in awe - really looked.

Papyrus’ entire skull was flushed orange, and his perfect form dripped with sweat. Sans stopped moving altogether, and his gaze wafted over every part of Papyrus’ body, lingering on the part where they connected. He pistoned his hips sharply, and his eyelights flicked up to watch his little brother’s ‘ _sex_ pression’ as he squirmed and writhed on his dick.

“…but they don’t get to see you l-like this…only i do.”

“Yes, Sans!”

“ you’re mine…ahhh o-oh god, Paps…Pappy~”

It was when Papyrus started swearing, begging, and demanding that Sans “fuck him into the Throne” that Sans lost what little control he had left.  
He’d never heard his little bro cuss before, and the shock of it caused his eye to glow once again, making the restraints go flying off the armrests with such force that they ended up on the crystal chandelier above. Papyrus instantly wrapped both of his arms and legs around his brother, drawing him as close as possible, their tongues finally meeting and clashing together as they started to come. Sans reached down between their bones to wrap his fingers around the glowing orange cock, his movements reaching speeds that neither of them knew he was even capable of.

_“SANS!! YES, FFFUUUUU-CK ME SANS PLEASEFUCK ME-!”_

  
Sans’ lights in his eyes flickered and then went out entirely, leaving his eyesockets empty and haunting. In his primal state, he shuddered violently, baring his fangs and sinking them almost tenderly into Papyrus’ neck, growling as he did so. The cartilage gave a little but did not draw blood, but as Papyrus’ hands scrabbled at the back of Sans’ skull, he pushed him into his neck further, begging for more. Harder. Deeper. Make it hurt. Feels too fucking good. Sans…Sans…fuck yes…

**“SANS!”**  
His legs locked them together as he felt the bulging dick inside of him expand, and the feeling of being so full made his insides clamp down on it. The fluttering pulsations of his orgasm made his canal spasm rhythmically, milking Sans’ cock for all it was worth and making sure he was forced to release inside. He’d be damned if he’d let Sans break his promise of not soiling his uniform now.

_“P-PAPS, OH MY FUCKING GOD. SCREAM IT FOR ME, BABY!”_

 

And scream he did, he screamed his brother’s name, apologies to Undyne, the Queen; heck, he might have even screamed his own name once. After all, he was very great, and as he released his seed all over his new uniform, he couldn’t help thinking that now, finally, he was officially a fully-fledged member of the Royal Guard.

And one who liked following traditions very, _very_ much.


End file.
